From owner-chemistry@ccl.net Thu Aug 16 02:44:00 2007 From: "Andreas Klamt klamt:cosmologic.de" To: CCL Subject: CCL: solvent calc. Message-Id: <-34939-070816024150-14119-htjth6KDOE13Obn5B+J3vg:-:server.ccl.net> X-Original-From: Andreas Klamt Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed Date: Thu, 16 Aug 2007 08:41:11 +0200 MIME-Version: 1.0 Sent to CCL by: Andreas Klamt [klamt[*]cosmologic.de] Hi Keith, normally the difference between solution phase and gasphase geometries is small. For consistency of the frequency calculations (which should be done in a local minimum geometry) you should do it on the gasphase geometry. More important than the change in geometry is the change in the kind of conformation which is the minimum in gasphase and solution (may be specific for each solvent). Within our COSMO-RS (COSMOtherm) methods I suggest the following procedure: 1) find the relevant conformations of the compounds (educts and products) in the gasphase and in the solvent and calculate their total energy with geometry optimization in the gasphase and in a virtual conductor (DFT/COSMO). We use BP-TZVP for this step. 2) Then get the total free energies of the compound in the gasphase and in the solvent (may even be a mixture, at variable temperature) from COSMOtherm (which also includes the Boltzmann averaging over the conformations). A potential shift in the preferred conformations in gasphase and solution is automatically taken into account in this step. 3) Now perform frequency calculations (probably good enough at DFT level) and higher lever calculations (if affordable, since DFT is unreliable for free energies of reactions) for the relevant conformations (Maybe the lowest conformers are sufficient in this step). 4) Finally correct the free energy of reaction (difference of educts and products) yielded from COSMOtherm by the difference of the vibrational contributions, and by the higher level to DFT differences of the representatives of educts and products taken into account in the higher level calculations. Andreas Keith Butler keeeto2000..yahoo.co.uk schrieb: > Sent to CCL by: Keith Butler [keeeto2000- -yahoo.co.uk] > > Dear Andreas, > > Just a follow up question to your answer. Would you > suggest that to find free energy of the solvated > species using an implict method that the frequency > calculations should be performed in the gas phase on > the SOLUTION phase geometries or on gas phase > structures before applying the thermodynamic cycle. > > Many Thanks, > > Keith Butler > > --- "Andreas Klamt klamt:-:cosmologic.de" > wrote: > > >> Sent to CCL by: Andreas Klamt >> [klamt###cosmologic.de] >> Dear Aleksandra, >> >> sorry to tell you that even in the case of neutral >> reactions it does not >> make much sense to apply the standard gasphase >> methods. All the >> vibrational free energy contributions are not >> meaningful in the solvent. >> The change in vibrational free energy from gasphase >> to the solvent is >> already parameterized into the solvent models (see >> e.g. my CCL >> contribution from 17.05.2007 ). >> >> In my opinion, the only reasonable way to do this in >> the solvent is to >> calculate the gasphase reaction and to apply >> dG_solvation (from a good, >> quantitative solvation model) to educts and >> products., i.e. use the >> thermodynamic cycle >> >> Educts, solv ---> Educts, gas --> Products,gas --> >> Products, solv >> >> Andreas >> >> >> Aleksandra Rudnitskaya aleksandra.rudnit001#umb.edu >> schrieb: >> >>> Sent to CCL by: "Aleksandra Rudnitskaya" >>> >> [aleksandra.rudnit001##umb.edu] >> >>> Thanks a lot to everyone who sent his answer. I >>> >> realized I took a wrong example. What if I choose >> the other system with benzene as a solvent? The >> questions are the same - >> >>> what should I write in input file for >>> >> optimization, and TS? >> >>> Thank you >>> >>> Aleksandra >>> >>> >>> >>>> Dear CCL members, >>>> >>>> Ive just started calculations with solvent. I >>>> >> decided to start from reaction of neutralization >> NaOH+HCl=H2O+NaCl. As I understand I should >> calculate >> >>>> 1) optimization sodium hydroxide in solvent >>>> >> (water); >> >>>> 2) optimization hydrochloric acid in solvent; >>>> 3) optimization sodium chloride in solvent; >>>> 4) transition state again in solvent. >>>> Idea is very similar to that when I calculate >>>> >> rxns in gas phase. Is it correct? >> >>>> When I calculate stable species without any >>>> >> solvent I use >> >>>> opt freq=noraman RHF/6-31G(d) >>>> For TS calculations I use >>>> RHF/6-31G(d) Opt(TS,CalcFC,noeigentest) >>>> >> Freq=noraman >> >>>> and then charge and multiplicity, and simple >>>> >> Z-matrix in specification part. How should input >> files look for optimization and searching TS? I know >> I have to use keyword SCRF, and one of those >> (SCRF=Dipole, PCM, DPCM, CPCM or IEFPCM), then >> specify solvent, and probably, dielectric constant >> somewhere in specification part after matrix. If you >> may guide me how to create input file itll help a >> lot. >> >>>> Thank you very much.> >>>> >>> >>> >>> >> -- >> >> > ----------------------------------------------------------------------------- > >> Dr. habil. Andreas Klamt >> COSMOlogic GmbH&CoKG >> Burscheider Str. 515 >> 51381 Leverkusen, Germany >> >> Tel.: +49-2171-73168-1 Fax: +49-2171-73168-9 >> e-mail: klamt[A]cosmologic.de >> web: www.cosmologic.de >> >> > ----------------------------------------------------------------------------- > >> COSMOlogic >> Your Competent Partner for >> Computational Chemistry and Fluid >> Thermodynamics >> >> > ----------------------------------------------------------------------------- > >> >> -= This is automatically added to each message by >> the mailing script =- >> To recover the email address of the author of the >> message, please change >> the strange characters on the top line to the : >> sign. 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Andreas Klamt COSMOlogic GmbH&CoKG Burscheider Str. 515 51381 Leverkusen, Germany Tel.: +49-2171-73168-1 Fax: +49-2171-73168-9 e-mail: klamt=-=cosmologic.de web: www.cosmologic.de ----------------------------------------------------------------------------- COSMOlogic Your Competent Partner for Computational Chemistry and Fluid Thermodynamics -----------------------------------------------------------------------------